ENGINEERING DATA
    1 ton a/c = 12,000 BTU per hour
    1 Boiler HP = 42,000 BTU input (@ approx. 80% efficiency)
    100 Boiler HP = 42 therm Input (@ approx. 80% efficiency)
    100 lb Steam = 1 therm (approx.)
    1 Engine HP = 10,000 BTU input (approx.)
    1 British Thermal Unit = Energy required to raise the temperature of 1 lb. Mass of water by 1° F
    1 SCF natural gas = 1,000 BTU (approx.)
    100 SCF natural gas = 1 therm (approx.)
    1 MSCF natural gas = 1,000 scf 1 MSCF = 10 therm
    1 Therm = 29.3 kilowatt hr
    Standard Cubic Foot = Volume of gas at standard conditions
    Standard conditions = 60° F @ 14.73 psia
    SCFH = Volume flow rate per hour @ standard conditions
    Degrees Celsius = 5/9 ( °F - 32)
ABBREVIATIONS
    ACSH - actual cubic feet per hour
    ACFM - actual cubic feet per minute
    BTU - British thermal unit
    MSCF - (thousand) standard cubic feet
    N.O. - Normally open
    N.C. - Normally closed
    PSI - pounds per square inch
    PSIA - pounds per square inch absolute
    PSIG - pounds per square inch gauge
    SCFH - Standard cubic feet per hour
    w.c. - inches of water column
    G - Gravity
    H - Pressure drop
    Q - Flow
    T - Temperature
    W - Flow rate
RULES OF THUMB - UNIT SIZING
    Sizing Boiler Feed or Condensate Return ump Discharge Pressure:
    1) If boiler < 50 psig, size pump to discharge 5 psig above working pressure.
    2) If boiler > psig, size pump to discharge 10 psig above working pressure.
    Sizing Boiler Feed or Condensate Return Pump Capacity:
    1) Condensate pump = 2 x condensate return rate
    2) Boiler Feed pump = 2 x boiler evaporation rate, or:
    a) .14 GPM/BHP (on/off pumps)
    b) .104 GPM/BHP (continuous running pumps)
    Receiver Storage:
    1) Size condensate receivers for 2 minute net storage capacity per return rate.
    2) Size boiler feed receivers for system capacity (normally estimated at 10 minutes)
RULES OF THUMB - GENERAL
    1 Ft3 Natural Gas = 1000 BTU
    1 Therm Natural Gas = 100,000 BTU
    1 Unit Natural Gas = 10 Therms = 1,000,000 BTU
    1 Ft3 Propane = 2,500 BTU
    1 Gallon #2 Oil - 140,000 BTU
    1 lb. Steam = 1000 BTU
    1 BHP = 42,000 BTU / hr Input
    1 BHP = 33,600 BTU / hr Output
    1 KWH Electric = 3412 BTU
    Normal Stack Temp on a 15 psig Steam Boiler = 375°F
    Normal Stack Temp on a 150 psig Steam Boiler = 475°F
    Normal Stack Temp on a 30 psig Hot Water Boiler = 340°F
    1 psig = 2.31' Head
    1 psig = 27.68" H20
    Air Supply Required (in CFM) = 10.8 X BHP
    Louver Size = 1 In2 per 4000 BTU (Input)

Conversion Factors - Download Excel file




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